The present invention relates to a composite magnetic body used to suppress electromagnetic interference brought about by interference from unwanted electromagnetic waves in a high-frequency band, and to an electromagnetic interference suppressing body obtained by the use thereof; and more particularly to a fireproofing technique for a composite magnetic body.
Cellular phones, personal computers, and other types of electronic equipment operated at high frequencies such as quasi-microwave band have become more widespread in recent years. In particular, smaller and lighter devices are urgently needed, with electromagnetic noise/interference posing a serious problem. In view of this, composite magnetic bodies and electromagnetic interference suppressing bodies are being commercialized as a means of countering such high-frequency electromagnetic interference.
Conventional composite magnetic bodies and electromagnetic interference suppressing bodies are disadvantageous, however, in that when a soft magnetic powder (particularly a soft magnetic alloy powder) and a binding agent are mixed together, flammability is promoted beyond the level possessed by the binding agent as such due to increased thermal conductivity or the catalytic action of the soft magnetic powder, making it extremely difficult to achieve self-extinguishing, which is the main element of fire resistance.
In view of this, the grain size of soft magnetic powder is normalized and soft magnetic powder is controlled to have a uniform grain size in conventional practice in order to achieve fire resistance characteristics of the composite magnetic body containing the soft magnetic powder.
However, the grain size of a powder merely indicates its dimensions and fails to unambiguously define the surface state of the powder (which determines aforementioned catalytic action or thermal conductivity), that is, the surface area in contact with air and other media.
In addition, fire resistance changes if the powder has a different grain size distribution.
In view of the above, it is an object of the present invention to provide a composite magnetic body containing a soft magnetic powder having a surface state defined in terms of specific surface area and thereby possessing the desired level of self-extinguishing, which is the main element of fire resistance.
It is another object of the present invention to provide an electromagnetic interference suppressing body by making use of the aforementioned composite magnetic body.
The inventor conducted thoroughgoing research into the relation between powder properties and fire resistance and discovered that the specific surface area of a soft magnetic powder has a marked effect on fire resistance. Specifically, the present invention, which is aimed at attaining the stated objects, entails using a soft magnetic powder normalized by the specific surface area and adding a fire retardant to a binding agent while taking into account the particle shape of the powder to fireproof the composite magnetic body and electromagnetic interference suppressing body.
According to an aspect of the present invention, there is provided a composite magnetic body comprising a soft magnetic powder and a binding agent, wherein the soft magnetic powder has a specific surface area of 0.1-3 m2/g.
According to another aspect of the present invention, there is provided an electromagnetic interface suppressing body for suppressing electromagnetic interference brought about by interference from unwanted electromagnetic waves by use of a composite magnetic body comprising a soft magnetic powder and a binding agent, wherein the soft magnetic powder has a specific surface area of 0.1-3 m2/g.